1. Field of the Invention
The present invention relates to a microphone apparatus.
2. Description of the Related Art
With a so-called camcorder, a lightweight television camera with an incorporated video cassette recorder, for example, sound around an object is recorded while the object is being pictured. In recording the sound, the microphone is designed so that only the sound coming from the direction of the object is recorded. That is, the camcorder is provided with a directional microphone that picks up the sound coming into the front of the camcorder.
One example of a microphone apparatus of this type is known as a "gun microphone." This microphone is provided, as shown in FIG. 1, with a pipe 2 extending from a diaphragm 1. The pipe 2 is provided with many through-holes 3 in its side wall, providing directionality so that the microphone is highly sensitive to a sound coming from its front and long along the center line of the pipe 2, or the opposite side of the diaphragm 1.
To be more specific, as shown in FIG. 1A, acoustic waves coming from the front of the microphone (the right-hand in the figure) have the same path length to the diaphragm 1 whether they arrive at it from the top of the pipe 2 or any one through-hole 3, so that they arrive in the same phase to be added together.
In contrast, as shown in FIG. 1B, acoustic waves coming from a side of the pipe 2 through different through-holes 3 differ in phase because their path lengths from the through-holes, or incident positions, to the diaphragm 1 are different. Likewise, as shown in FIG. 1C, an acoustic wave coming from the backside of the microphone arrives via different through-holes 3 at the diaphragm 1, causing a phase difference in the acoustic wave, or an incident signal. A plurality of holes 3 in the pipe 2 are arranged so that incident acoustic signals weaken each other. The microphone shown in FIG. 1 has a directionality in which sensitivity is low to acoustic waves coming from the side or back of the pipe.
Thus, the gun microphone as shown in FIG. 1 provides a directional microphone having a high sensitivity to an acoustic wave coming from the front of the microphone.
However, as described above, this microphone requires a pipe 2, which is long, thereby increasing the microphone's external dimensions.
Additionally, this unidirectional microphone has a high sensitivity only to acoustic waves coming from the front of the microphone, providing fixed, inflexible directionality. This makes it difficult to record not only sound coming from the desired direction of source, but also sound coming, for example, from the sides of the camcorder.